Prior art efforts in cigarette making have looked fairly extensively to the use of carbonized matter as a partial or total substitute for the customary tobacco shred content of cigarettes. Viewing such efforts as endeavors to reach equality in smoking experience between carbon-substitute cigarettes and conventional cigarettes as respects resistance to draw, ash-forming and ash-release, applicants herein have concluded that such prior art efforts have fallen short of reaching such equality. Various observations underlie such conclusion of applicants as are now specifically noted.
In the selection of carbonized matter for processing with tobacco, opposed observations apply as to selection of fiber dimension. In blending of tobacco shreds and fine-dimensioned carbon fibers, gravimetric sedimentation in processing lessens initial carbon content in uncontrolled measure giving rise to blend inconsistency. Processing of brittle thin fibers itself leads to the formation of dust-like carbon particles which can either fall out of the blend or agglomerate in the cigarette filter, clogging the filter. Although a graphitization treatment of carbon fibers will overcome their brittleness, this practice incurs a prohibitive cost and still does not fully overcome the above-noted adverse effect of sedimentation. Because the composition of such blends cannot be maintained constant in the course of processing thereof, difficulties are encountered in the recovery and reuse of filler from off-standard cigarettes.
While gravimetric sedimentation of carbon in blend processing is avoided by selection of large-sized carbon fibers, such as may be derived from the carbonization of wood shreds (excelsior) having an average diameter of one millimeter, carbon fibers present in the formed blended cigarette rod having a thickness greater than 0.3 millimeter generate fiery particles which drop freely from the cigarette coal in the course of smoking.
The difficulties attendant on processing a blend of tobacco shreds and carbonized matter, particularly sedimentation, are seemingly avoided by the formation of cigarettes comprised fully of carbonaceous matter. Here, however, it is applicants' observation that prior art practices yield fully carbon smoking products having porosity considerably lower than the porosity of conventional cigarettes. As a consequence, the resistance-to-draw of the rod is excessively high. This category of prior art efforts has the evident further task of attaining flavor without benefit of tobacco content. Further prior art teachings suggest the use of carbonized rod structures comprised of large-sized structural elements which upon burning will generate the aforementioned fiery particles. Such rod structures are also difficult to cut to proper lengths for use in cigarettes.